Backrest for chair

ABSTRACT

A backrest for a chair, including a bag-like upholstery material, with which a back frame is upholstered by fitting the bag-like upholstery material onto the back frame that has a pair of right and left side frames extending in an up-down direction. A high-friction member is disposed on at least one of an inner surface of both side portions of the upholstery material on a lower portion side thereof supporting the sitting person around the hip and an outer surface of the right and left side frames contacting the inner surface of the side portions of the upholstery material on a lower portion side thereof, the high-friction member being configured to increase the sliding resistance in an area of contact between the upholstery material and the side frames

FIELD

The present invention relates to a backrest for a chair, the backresthaving a back frame upholstered with a bag-like upholstery material byfitting the bag-like upholstery material onto the back frame.

BACKGROUND

This type of backrest is discussed in Patent Literatures 1 and 2, forexample.

CITATION LIST Patent Literature

Patent Literature 1: European Patent Application Publication No. 0922419

Patent Literature 2: Japanese Patent Application Laid-open No.2003-135200

SUMMARY Technical Problems

As a bag-like upholstery material for the backrests described in PatentLiteratures 1 and 2, a meshed woven material of synthetic fibers isoften used from the viewpoint of ventilation, stretch properties, andtensile strength, for example.

When such an upholstery material is used to upholster a back frame byfitting the upholstery material onto the back frame in a predeterminedtensioned state and a sitting person falls back on the backrest, aback-surface portion of the upholstery material positioned to the rearof the back frame is pulled around to the front-surface side of theupholstery material so that a front-surface portion of the upholsterymaterial positioned to the front of the back frame can be appropriatelywarped backward.

At that time, if the sliding resistance at the area of contact betweenlower portions of side portions of the upholstery material and outersurfaces of right and left side frames of the back frame is small, thelower portions of the side portions of the upholstery material may moveup and slackening or development of wrinkles may be caused.

Further, if the sliding resistance at the area of contact between thelower portions of the side portions of the upholstery material where thesitting person is supported around the hip and the outer surfaces of theside frames is small, the lower portions of the side portions of theupholstery material are easily moved around toward the front surfaceside. Thus, the front-surface portion of the upholstery material wherethe sitting person is supported around the hip is excessively warpedbackward, the lumbar support effect cannot be obtained, and the hip ofthe sitting person cannot be comfortably supported.

The present invention has been made in view of the foregoing problems,and an object of the present invention to provide a backrest for a chaircapable of preventing, by making lower portions of side portions of anupholstery material less slidable on side frames, slackening ordevelopment of wrinkles due to moving up of the upholstery material, andalso preventing a front-surface portion of the upholstery material beingexcessively warped backward, so that the hip of the sitting person canbe comfortably supported.

According to the present invention, the above object is accomplished bythe following aspects.

(1) A backrest for a chair, comprising a bag-like upholstery material,with which a back frame is upholstered by fitting the bag-likeupholstery material onto the back frame that has a pair of right andleft side frames extending in an up-down direction, wherein ahigh-friction member is disposed on at least one of an inner surface ofboth side portions of the upholstery material on a lower portion sidethereof supporting the sitting person around the hip and an outersurface of the right and left side frames contacting the inner surfaceof the side portions of the upholstery material on a lower portion sidethereof, the high-friction member being configured to increase thesliding resistance in an area of contact between the upholstery materialand the side frames.

According to the above-described configuration, because the lowerportions of the side portions of the upholstery material is made lessslidable, moving up of the upholstery material to cause slackening ordevelopment of wrinkles can be prevented.

Further, because the lower portions of the side portions of theupholstery material is made less movable around toward the front surfaceside of the back frame, the front-surface portion of the upholsterymaterial on a lower side thereof where the sitting person is supportedaround the hip is prevented from being excessively warped backward, sothat the hip of the sitting person can be comfortably supported by thelumbar support effect.

(2) In the above-described aspect (1), stitched portions are formed byinternally folding and stitching both side-end portions of theupholstery material to cause the upholstery material to be bag-like,each of the stitched portions being covered by a side-end portion of thehigh-friction member fixed by stitching.

According to the above-described configuration, the stitched portion ofthe side-end portions of the upholstery material is covered with theside-end portion of the high-friction member by stitching. Thus, thestitched portion of the side-end portions of the upholstery material canbe reinforced, so that the upholstery material can be prevented frombeing frayed.

Because the lower portions of the upholstery material can slide withrespect to the side frames via the high-friction member affixed to theinner surface of the side portions of the upholstery material, wearingof the side portions of the upholstery material can be reduced, so thatthe reupholstering intervals of the upholstery material can be extendedand cost can be reduced.

(3) In the above-described aspect (1) or (2), the high-friction memberis formed by one of a polyurethane resin or a foam thereof, a urethaneelastomer, and rubber.

According to the above-described configuration, all of the recitedmaterials are preferable for the low-friction member or thehigh-friction member, readily formable, and highly versatile. Thus, thestructure can be relatively inexpensively implemented.

Advantageous Effects of Invention

The present invention provides a backrest for a chair capable ofpreventing slackening or development of wrinkles due to moving up of theupholstery material, and also preventing a front-surface portion of theupholstery material being excessively warped backward, so that the hipof the sitting person can be comfortably supported.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a side view of a chair equipped with a backrest according toan embodiment of the present invention in a standby state.

FIG. 2 is a side view of the chair of FIG. 1 in a seated state.

FIG. 3 is a perspective view of the backrest as seen from diagonallybehind, in a state before a back frame is upholstered with an upholsterymaterial.

FIG. 4 is an enlarged cross section taken along line IV-IV of FIG. 1.

FIG. 5 is an enlarged cross section taken along line V-V of FIG. 1.

FIG. 6 is an enlarged view of a portion A of FIG. 4.

FIG. 7 is an enlarged view of a portion B of FIG. 5.

FIG. 8 is an enlarged cross section illustrating a manner of attaching alow-friction member and a high-friction member to the back frameaccording to a variation.

FIG. 9 is an enlarged cross section illustrating a manner of attachingthe low-friction member and the high-friction member to the back frameaccording to another variation.

DESCRIPTION OF EMBODIMENTS

In the following, embodiments of the present invention will be describedwith reference to the drawings.

FIGS. 1 and 2 are side views of a chair including a backrest accordingto an embodiment of the present invention. The chair includes a lowerassembly 4 which includes a disk-shaped base 1, a leg column 2 mountedat the center of the disk-shaped base 1 in an upright manner, and asupport base 3 fixedly mounted on an upper end of the leg column 2.

The support base 3 has a substantially triangular shape expanding fromthe upper end of the leg column 2 toward the front in plan and sideviews.

At the front end of the support base 3, a front-lower portion of a seat5 is pivotally mounted on a base axle 6 extending in a left-rightdirection. The seat 5 can be rotated about the base axle 6 into astandby position in which the seat 5 is inclined with its rear raised,as illustrated in FIG. 1, or into a use position in which the seat 5 ishorizontal or inclined with its rear slightly lowered, as illustrated inFIG. 2.

On both sides of the rear of the seat 5, a pair of right and left armrests 7 are integrally formed.

The arm rests 7 extend upward from the sides of the rear of the seat 5and include a backrest pivotal support portion 7 a and an arm padportion 7 b. The backrest pivotal support portion 7 a includes a curvedsurface 8 protruding backward and having a semicircular or fan shape ina side view, which shape is centered about a support axle 11 of abackrest 9, which will be described later. The arm pad portion 7 bextends forward from an upper portion of the backrest pivotal supportportion 7 a and has an upwardly arched shape. Thus, the arm rests 7 havea generally forwardly extending triangular shape converging in aforward-upper direction in a side view.

The arm pad portions 7 b may be dimensioned with respect to thefront-rear direction such that front-end portions of the arm padportions 7 b are positioned forwardly of a vertical line S passingthrough the center of the base axle 6, on which the seat 5 is pivoted,in the standby position illustrated in FIG. 1.

When the seat 5 is in the use position as illustrated in FIG. 2, thefront-end portions of the arm pad portions 7 b may be positionedslightly to the rear of the vertical line S corresponding to the baseaxle 6 on which the seat 5 is pivoted.

On outer surfaces of slightly forward portions of the backrest pivotalsupport portions 7 a of the right and left arm rests 7, front-endportions of forwardly extending side pieces 10 extending forward from alower portion of the backrest 9 on both sides are located. The front-endportions are pivoted on the support axle 11 extending substantially inthe left-right direction. Thus, the backrest 9 can be rotated about thesupport axle 11 into an upright position illustrated in FIG. 2 or abackwardly inclined position, not illustrated, with respect to the seat5 and the arm rests 7.

The backrest 9 includes a concave surface 12 facing the rear surface ofthe backrest pivotal support portions 7 a and having an arch shapesubstantially complementary to the curved surface 8 on the rear surfaceof the backrest pivotal support portions 7 a. Thus, the backrest 9 canbe rotated about the support axle 11 with the opposed surfacespositioned close to each other. Between a central portion of a lowerframe 20, which will be described later, of the backrest 9 with respectto the left-right direction and an upper surface of the front-endportion of the support base 3, a first biasing portion 13 for biasingthe backrest 9 in an upright direction is provided. Examples of thefirst biasing portion 13 may include a gas spring and a compressionspring.

The support base 3 includes a second biasing portion 14 for helping thesitting person stand up by biasing the seat 5 into the standby position.

The second biasing portion 14 includes a rubber torsion unit 15 havingan axis in the left-right direction; a backwardly extending first link16 linked with the rubber torsion unit 15 and biased in theanticlockwise direction in the side view of FIG. 1; and a second link 17having a lower-end portion pivoted to the end of the first link 16 viaan axis extending in the left-right direction. An upper end portion ofthe second link 17 is pivoted on a lower surface of the seat 5 in anintermediate area in the front-rear direction via an axis extending inthe left-right direction, the second link 17 extending in a diagonallyupward-rear direction.

As illustrated in FIG. 3, the backrest 9 extends in the up-downdirection and includes a back frame 22 having a vertically longerrectangular shape in a front elevation. The back frame 22 includes apair of right and left side frames 18 extending in the up-down directionand having a gradually increasing front-rear dimension toward the lowerends with which the forwardly extending side pieces 10 are continuouslyconnected. The upper ends of the side frames 18 are coupled via an upperframe 19 extending in the left-right direction. The lower ends of theside frames 18 are coupled via a lower frame 20 extending in theleft-right direction. The upper frame 19 and the lower frame 20 arecoupled at their intermediate portions in the left-right direction viaan intermediate frame 21 which is positioned backwardly of the sideframes 18 and extending in the up-down direction.

The back frame 22 may be integrally formed from a synthetic resinmaterial having an appropriate elasticity. Preferably, the syntheticresin material may contain reinforced fibers, such as glass or carbonfibers, for increased strength.

The lower portions of the side frames 18 and a lower portion of theintermediate frame 21 are arched with the center of curvature locatedforwardly in a side view. The upper frame 19 and the lower frame 20 arecurved in a plan view, with their intermediate portions positionedbackwardly of their side portions. Thus, when the back frame 22 isupholstered with a bag-like upholstery material 26 as will be describedlater, a front-surface portion and a back-surface portion of theupholstery material 26 with respect to the back frame 22 are allowed tobe relatively greatly spaced apart from each other in the front-reardirection.

Further, the lower portion of the backrest 9 is also backwardly spacedfrom the rear ends of the seat 5 and the arm rests 7. Thus, when thebackrest 9 is rotated, interference with the rear ends of the seat 5 andthe arm rests 7 is prevented, so that the backrest 9 can have a largerange of backward rotation.

The intermediate frame 21 may be thinner than the other frame formingmembers of the back frame 22 so that the intermediate frame 21 can bemore readily elastically deformed than the other members. In this way,when the front-surface portion of the upholstery material 26 issubjected to a load as will be described later, the intermediate frame21 can be elastically deformed in the forward direction.

At the upper end of the back frame 22, a head-rest frame 25 isintegrally formed. The head-rest frame 25 includes upwardly extendingextension frames 23 which are curved with intermediate portions thereofpositioned forwardly of the upper and lower portions thereof in a sideview. Upper ends of the extension frames 23 are coupled to each othervia a top frame 24 extending in the left-right direction.

As illustrated in FIG. 3, the back frame 22 and the head-rest frame 25are upholstered from above with the bag-like upholstery material 26 byfitting the bag-like upholstery material 26 onto the back frame 22 andthe head-rest frame 25. The upholstery material 26 includes openings inthe lower end and lower-side portions, and has stretch properties. Theupholstery material 26 may be in the form of a mesh woven from syntheticfibers. The upholstery material 26 includes a head-rest covering portion27 covering the head-rest frame 25, and a backrest covering portion 28covering the back frame 22.

The back frame 22 and the head-rest frame 25 are covered with theupholstery material 26 in a predetermined tensioned state. The right andleft forwardly extending side pieces 10 protrude in the forwarddirection through the lower-side openings of the upholstery material 26.Lower-end portions of a front-surface portion 28 a and a back-surfaceportion 28 b of the upholstery material 26 positioned to the front andrear of the back frame 22, respectively, are joined to each other via ajoining means below the lower frame 20 of the back frame 22. Examples ofthe joining means include hook-and-loop fasteners, hooks, and zippers(not illustrated).

When the head rest is not required, the head-rest frame 25 and thehead-rest covering portion 27 of the upholstery material 26 may beomitted.

As illustrated in FIGS. 3 to 7, thin and flexible low-friction members29 having small sliding resistance with respect to the frames 18 and 23are disposed on inner surfaces of the side portions of the upholsterymaterial 26 that contact outer surfaces of the side frames 18 of theback frame 22 excepting the forwardly extending side pieces 10, andouter surfaces of the extension frames 23 of the head-rest frame 25.

Thin and flexible high-friction members 30 having large slidingresistance with respect to the side frames 18 are disposed on innersurfaces of the side portions of the upholstery material 26 where thesitting person is supported around his or her hip, the inner surfacescontacting the outer surfaces of lower portions of the side frames 18.

Preferably, the low-friction members 29 may include a material such as apolyamide resin (trade name Nylon), fluororesin (Teflon (registeredtrademark); trade name Daiflon), or polyacetal. The high-frictionmembers 30 may include a material such as a polyurethane resin or a foamthereof, a urethane elastomer, or rubber.

As illustrated in enlarged cross sections of FIGS. 6 and 7, the side-endportions of the upholstery material 26 are inwardly folded into layersand stitched into bag-shaped portions at positions close to the innersurfaces on the front side of the right and left side frames 18 orextension frames 23. At the same time, the front-end portions of thelow-friction member 29 and the high-friction member 30 are folded intoU-shaped portions by which the folded portions of the upholsterymaterial 26 are covered by stitching. In this way, stitched portions 26a of the side-end portions of the upholstery material 26 can bereinforced. The front-end portions of the low-friction member 29 and thehigh-friction member 30 may be simply stitched onto the stitchedportions 26 a of the side-end portions of the upholstery material 26simultaneously without being folded in U-shape.

The low-friction member 29 and the high-friction member 30 may beaffixed onto the outer surfaces of the side frames 18 and the extensionframes 23 or onto the inner surfaces of the side portions of theupholstery material 26 by using an adhesive, rather than by stitching.

As illustrated in FIG. 8, a concave groove 31 may be formed in the outersurfaces of the side frames 18 and the extension frames 23 in theup-down direction, and a convex portion 32 may be formed on innersurfaces of the low-friction member 29 and the high-friction member 30in the up-down direction. In this way, by fitting the convex portion 32in the concave groove 31, the low-friction member 29 and thehigh-friction member 30 can be detachably mounted on the outer surfacesof the side frames 18 and the extension frames 23.

Further, as illustrated in FIG. 9, the low-friction member 29 and thehigh-friction member 30 configured to be elastically deformable may bedetachably fitted on the outer surfaces of the side frames 18 and theextension frames 23. In this case, the concave groove 31 illustrated inFIG. 8 may not be provided in the side frames 18 and the extensionframes 23.

The low-friction member 29 and the high-friction member 30 may be a filmformed on the outer surfaces of the side frames 18 and the extensionframes 23 by coating.

When the sitting person falls back on the backrest 9 structured asdescribed above, the back-surface portion 28 b of the upholsterymaterial 26 is pulled and extended as the front-surface portion 28 a ofthe upholstery material 26 is extended and warped backward, as indicatedby the two-dot chain line in FIG. 4. As a result, the side portions ofthe upholstery material 26 are pulled around toward the front-surfaceportion 28 a to some extent, as indicated by arrows, so that the amountof warping of the front-surface portion 28 a in the backward directionincreases. At this time, because the low-friction members 29 attached tothe inner surfaces of the side portions of the upholstery material 26are in contact with the outer surfaces of the side frames 18 except forthe lower portions thereof and with the outer surfaces of the extensionframes 23, the sliding resistance at their areas of contact is reduced.

Consequently, the upper side portions of the upholstery material 26 arepermitted to smoothly move around toward the front surface side, so thatthe front-surface portion 28 a of the upholstery material 26 supportingthe back and head of the sitting person can be effectively warpedbackward in such a manner as to fit the back and head of the sittingperson. Thus, the back and head of the sitting person can be comfortablysupported with flexibility.

Also, the development of unpleasant sliding noise can be prevented whenthe side portions of the upholstery material 26 are moved around towardthe front-surface portion 28 a.

Further, because the upholstery material 26 slides with respect to theside frames 18 via the low-friction members 29 affixed on the innersurfaces of the side portions of the upholstery material 26, wearing ofthe side portions of the upholstery material 26 can be reduced, so thatthe reupholstering intervals can be extended and cost can be reduced.

On the other hand, the high-friction members 30 are attached to theinner surfaces of the side portions of the upholstery material 26 wherethe sitting person is supported around the hip, the inner surfacescontacting the outer surfaces of the lower portions of the right andleft side frames 18. Thus, the sliding resistance between the sideframes 18 and the lower side portions of the upholstery material 26 isincreased.

As a result, even when the lower portions of the side frames 18 arecurved into an arch shape extending forward, the lower portions of theside portions of the upholstery material 26 are prevented from movingup, thus preventing slackening or development of wrinkles in the lowerportion of the upholstery material 26.

Further, because the movement of the lower side portions of theupholstery material 26 toward the front side of the back frame 22 isprevented or reduced, the lower portion of the front-surface portion 28a of the upholstery material 26 where the sitting person is supportedaround the hip can be maintained in a properly tensioned state andprevented from being excessively warped backward. Thus, the lumbarsupport effect can be obtained and the hip of the sitting person can becomfortably supported, thereby providing enhanced comfort to the sittingperson.

In the embodiments illustrated in FIGS. 8 and 9, the side portions ofthe upholstery material 26 can slide with respect to the low-frictionmember 29 and the high-friction member 30 attached to the side frames18. Thus, effects similar to those described above can be obtainedbecause of the small and large sliding resistances provided between theupholstery material 26 and the side frames 18.

The present invention is not limited to the foregoing embodiments andmay include various other modifications or implementations.

For example, while the low-friction members 29 are attached to the innersurfaces of the upper side portions, excluding the lower side portionsof the upholstery material 26, the low-friction members 29 may beomitted and only the high-friction members 30 may be provided.

In the foregoing embodiments, the high-friction members 30 may bedisposed on the inner surfaces of the side portions of the upholsterymaterial 26 or on the outer surfaces of the side frames 18. Thehigh-friction members 30 may be disposed on both the outer surfaces ofthe side frames 18 and the inner surfaces of the side portions of theupholstery material 26, so that the high-friction members 29 can becontacted with each other.

The present invention may be applied to the backrest for conventionalchairs having the seat 5 that is not inclined up or down.

REFERENCE SIGNS LIST

1 BASE

2 LEG COLUMN

3 SUPPORT BASE

4 LOWER ASSEMBLY

5 SEAT

6 BASE AXLE

7 ARM REST

7 a BACKREST PIVOTAL SUPPORT PORTION

7 b ARM PAD PORTION

8 CURVED SURFACE

9 BACKREST

10 FORWARDLY EXTENDING SIDE PIECE

11 SUPPORT AXLE

12 CONCAVE SURFACE

13 FIRST BIASING PORTION

14 SECOND BIASING PORTION

15 RUBBER TORSION UNIT

16 FIRST LINK

17 SECOND LINK

18 SIDE FRAME

19 UPPER FRAME

20 LOWER FRAME

21 INTERMEDIATE FRAME

22 BACK FRAME

23 EXTENSION FRAME

24 TOP FRAME

25 HEAD-REST FRAME

26 UPHOLSTERY MATERIAL

26 a STITCHED PORTION

27 HEAD-REST COVERING PORTION

28 BACKREST COVERING PORTION

28 a FRONT-SURFACE PORTION

28 b BACK-SURFACE PORTION

29 LOW-FRICTION MEMBER

30 HIGH-FRICTION MEMBER

31 CONCAVE GROOVE

S VERTICAL LINE

1. A backrest for a chair, comprising a bag-like upholstery material,with which a back frame is upholstered by fitting the bag-likeupholstery material onto the back frame that has a pair of right andleft side frames extending in an up-down direction, wherein ahigh-friction member is disposed on at least one of an inner surface ofboth side portions of the upholstery material on a lower portion sidethereof supporting the sitting person around the hip and an outersurface of the right and left side frames contacting the inner surfaceof the side portions of the upholstery material on a lower portion sidethereof, the high-friction member being configured to increase thesliding resistance in an area of contact between the upholstery materialand the side frames.
 2. The backrest for a chair according to claim 1,wherein stitched portions are formed by internally folding and stitchingboth side-end portions of the upholstery material to cause theupholstery material to be bag-like, each of the stitched portions beingcovered by a side-end portion of the high-friction member fixed bystitching.
 3. The backrest for a chair according to claim 1, wherein thehigh-friction member is formed by one of a polyurethane resin or a foamthereof, a urethane elastomer, and rubber.